Adding image to graphic frame that is within a text frame

I know I had the answer to this many moons ago but I have forgotten the answer. If I want to add an image to a graphics frame that is within a text frame I need to do something special otherwise I get a blank section on the page. I can’t find the answer by searching. Help please ?

Select the edge of the frame, then press Return (rather than double-click).

If you can’t easily select the graphics frame edge, navigate to it from another handle on another frame.

Many thanks Lillie!